1. Field of the Invention
The present invention relates to a piezoelectric laminate stack constructed by laminating a plurality of plate members made of a piezoelectric element, which expand and contract according to an electric voltage applied thereon to operate as an actuator.
2. Description of the Related Art
A conventional piezoelectric laminate stack comprises piezoelectric circular disk-type plates having electrodes formed on both faces, and metal plates approximately the same shape as the piezoelectric plates having one projection on its periphery, as proposed by U.S. patent application No. 621,624. The piezoelectric plates and metal plates are stacked alternately, and in such a manner that the projections of each metal plate lie in a direction opposite to that of the projections formed on the metal plate positioned adjacent thereto. Each projection is electrically connected to another projection positioned alternately to the former projection, and positive or negative electrodes are connected to each projection. In such a piezoelectric laminate stack, however, since the piezoelectric plates can displace in a radial direction relative to the metal plates, it is difficult to keep the stack in its proper formation and operation becomes difficult unless the stack is housed in a housing immediately after stacking is completed, or the stack is formed directly in the housing. In these cases, the piezoelectric plates used for this conventional piezoelectric stack body must be previously polarized, raising the production cost of the stack. Further, while this kind of piezoelectric stack is usually subjected to a high voltage, to obtain a larger displacement of the stack, two adjacent metal plates may come to face each other without the insulation provided by the piezoelectric plates, as these piezoelectric plates are displaced in a radial direction, and thus an empty gap is formed between the two metal plates and an electrical discharge occurs between the poles of the metal plates.